The present invention relates generally to variable reluctance sensors.
Modern motor vehicles are equipped with numerous sensors that enhance the safety and quality of the vehicle operation. Some of these sensors are variable reluctance (VR) sensors that translate mechanical motion into electrical signals that can be useful, e.g., knowing the angular position and angular speed of an engine crank. VR sensors generate their own electrical pulses and as such, a supply voltage is not required.
In general, a typical VR sensor assembly includes a coil wound around a spool. The spool is disposed around a metal pole piece and a magnet is placed in proximity to the pole piece, e.g., adjacent to the end of the pole piece. The magnet creates a magnetic flux field around the pole piece and the coil. A target wheel, usually associated with rotating part, e.g., a crank shaft, is placed near the end of the VR sensor. The target wheel includes plural teeth and as it rotates, the teeth induce changes in the magnetic flux field that cause the coil to generate electrical pulses that correspond to the changes in the magnetic flux field. Accordingly, the electrical pulses can be processes to determine the angular position and angular speed of the, e.g., crank shaft.
As described above, VR sensors do not include any moving parts internal to the sensor. The output performance of VR sensors depends on the number of wire turns and the rate of flux changes over time. This relationship is given by the formula:
V=(N*dxc3x8/dt)
where:
V is the voltage output by the sensor;
N is the number of wire turns in the coil; and
dxc3x8/dt is the rate of change of the flux over time.
As recognized by the present invention, it is possible to magnetize the spool, eliminate the need for a separate magnet, and achieve the same functionality as current VR sensors.
A sensor assembly includes a spool that has magnetic filaments disposed therein. The magnetic filaments are magnetized to create a magnetic flux around the spool. A coil is wound around the spool and the coil is disposed within the magnetic flux generated by the spool. Also, a pole piece is disposed within the spool.
Preferably, the sensor assembly further includes a target wheel that rotates relative to the sensor assembly. In a preferred embodiment, the target wheel induces changes in the magnetic flux. These changes in the magnetic flux are sensed by the coil as the target wheel rotates. In a preferred embodiment, the coil is electrically connected to a microprocessor that receives signals representing changes in the magnetic flux density sensed by the coil. The microprocessor processes the signals to determine the relative motion between the target wheel and the sensor assembly.
In a preferred embodiment, the magnetic piece has a elliptical cross-section.
Preferably, the sensor assembly includes a rotating vehicle part that is connected to the target wheel and a stationary vehicle part that is connected to the sensor assembly. The microprocessor determines the relative motion between the rotating part and the stationary part. Preferably, the magnetic filaments are evenly dispersed throughout the spool, but they can also be unevenly dispersed throughout the spool.
In another aspect of the present invention, a variable reluctance sensor assembly includes a magnetic spool with a coil disposed therearound. The magnetic spool generates a magnetic flux field around the coil. In this aspect of the present invention, a target wheel is rotatably disposed adjacent to the spool. The target wheel is configured so that it rotates adjacent to the spool it induces changes in the magnetic flux field sensed by the coil.
In yet another aspect of the present invention, a variable reluctance sensor assembly includes a spool that has a coil disposed therearound. The spool includes means for allowing the spool to be magnetized so that the spool generates a magnetic flux field around the coil. In this aspect, the variable reluctance sensor also includes means for inducing changes in the magnetic flux field sensed by the coil.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: